Installation for the control of crack formation in concrete structures



May 28, 1968 c. l. WILLIAMS 3,385,017

INSTALLATION FOR THE CONTROL OF CRACK FORMATION IN CONCRETE STRUCTURES Filed June 10 1965 INVENTOR. CHESTER I. W/LL/AMS United States Patent 3,385,017 INSTALLATION FOR THE CONTROL OF CRACK FORMATION IN CONCRETE STRUCTURES Chester I. Williams, 347 Greenbriar, SE., Grand Rapids, Mich. 49506 Filed June 10, 1965, Ser. No. 462,825 4 Claims. (Cl. 52-378) ABSTRACT OF THE DISCLOSURE Devices for the control of the formation of cracks in concrete by positioning resilient strips at the surface plane of horizontal slabs with adjustable legs supporting a stiffening member extending along the edge of the strips, and by the installation of reinforcing rods traversing at a nonperpendicular angle a vertical fracture plane defined by strips secured to wall-forming panels.

This invention relates to equipment used in the formation of concrete structures. All masonry materials undergo dimensional changes as a result of variation in moisture, temperature, and occasionally due to the shifting of support areas and footings. These changes are accompanied by stresses of considerable magnitude, as there is rarely suiiicient freedom of movement for the concrete structure to accommodate itself to these changes. These factors make it inevitable that cracks will develop in any concrete structures of substantial size, and it is common practice to anticipate this condition by controlling the particular point at which the cracks are to take place.

Lines of weakness across the surface of a concrete structure are commonly established by embedding rubber strips at the surface of the concrete, and the presence of these strips will interrupt the continuity of the concrete mass at this point to provide localized weakness and stress concentration in this area. The crack will therefore begin below the strip, and normally will proceed in close proximity to a plane perpendicular to the surface of the concrete and will extend along underneath the strip. The strip can therefore function in some respects both as a seal and as a means for concealing the crack.

This invention provides a device for positioning a rubber crack-control strip for a concrete slab which is usually (but not necessarily) poured upon a graded ground surface. In the preferred form of the invention, the supporting device for the strip is formed of a continuous piece of sheet steel, and with a central portion adapted to grip a stiffening back normally provided on the control strip. The strip will normally extend upwardly from this stiffening back, and the preferred supporting device is equipped with legs which can function as stakes to be shoved into the ground. These are readily adjustable with regard to depth of penetration to determine the correct vertical position of the control strip so that the top edge of it is coplanar with the poured surface of the concrete.

It is often necessary to control the amount of separation between portions of a concrete structure on opposite sides of a crack. This invention provides a system for retaining the relative position of the separated portions of the concrete structure, while providing limited interference with the crack formation. Many concrete structures are provided with submerged reinforcing rods, and the control of crack formation in a wall (for example) containing such rods is provided by interrupting the reinforcing rods at a point adjacent the desired plane of crack formation. This plane is established preferably by the presence of rubber-like control strips installed at opposite sides of the wall so that the crack is then formed approximately on a plane containing both of these parallel strips. In a wall, this plane will normally be established in a vertical "ice position, and the horizontal series of reinforcing rods will be halted at a point adjacent this plane. To control separation of the opposite portions of the concrete structure at this plane, and also to prevent any undesirable degree of shifting along the plane of the crack, a group of auxiliary reinforcing rods are installed at an angle of preferably sixty degrees to the plane determined by the two parallel control strips. These rods are comparatively short (such as from two to four feet in length, and extend approximately the same distance on opposite sides of the crack plane). These rods are preferably crimped into an undulating pattern, which has a double value. The crimped conformation increases the retention in the sound concrete, and yet provides a limited degree of extensibility at the point where the crack has formed. With this arrangement, considerable elongation of the auxiliary rods can be provided without disrupting the retention of the rods in the concrete mass on either side of the crack. Essentially this same feature can be provided in horizontal slabs poured on a graded ground surface by placement of the auxiliary rods at an angle of approximately sixty degrees to a vertical plane passing through the control strips referred to above. This can be done whether or not the slab is equipped with reinforcing rods; but if the slab is thus reinforced, the rods should be interrupted at the predetermined crack plane as previously described.

The several features of the invention will be analyzed in further detail through a discussion of the embodiments illustrated in the accompanying drawing. In the drawing:

FIGURE 1 presents a perspective view in section showing the installation of the preferred form of the supporting devices for positioning a control strip for a concrete slab poured on a ground surface.

FIGURE 2 is a sectional elevation on an enlarged scale showing one of the supporting devices illustrated in FIG- URE l, and also illustrating the position of auxiliary reinforcing rods that may be used in conjunction with this device.

FIGURE 3 is a plan view showing the installation of one of the reinforcing strips shown in FIGURE 1, prior to forcing the legs of the device into the ground.

FIGURE 4 is a side elevation showing the installation of the section of supported control strip illustrated in FIGURE 3.

FIGURE 5 is a section on an enlarged scale showing the manner of securing a control strip to a form panel preparatory to pouring a wall structure.

FIGURE 6 illustrates a reinforced wall structure as formed by panels to which controls strips have been secured as shown in FIGURE 5, and illustrating the installation of auxiliary reinforcing rods and the interruption of the primary reinforcing rods at the crack plane.

The concrete slab indicated at '10 in FIGURE 1 is shown as poured on a graded ground surface 11. Prior to the pouring of the concrete 10, a group of crack-control strips as shown at 12-14 is installed, with the top edges of the strips co-planar with the top surface of the slab 10, as shown in FIGURE 2. The strips themselves include the elongated sections of rubber-like material shown at 15 in FIGURE 2, and these are preferably slightly narrower at the top edge than at the bottom edge. The top edge 16 is preferably concave to maintain an effective seal against a form panel 17, when the device is used in the formation of vertical walls. When used in conjunction with pouring slabs, it is preferable to leave the top edge 16 flat, as shown in FIGURE 2, to provide a better reference surface. The strips are then secured in position by nails as shown at 18 in FIGURE 5.

The strips 12-14 are provided with a stiffening back 19 in the form of a channel embracing the lower edge, and this channel forms a beam extending between the supporting devices generally indicated at 20 in FIGURE 2. These devices have a central U-shaped portion 21, and the sides of this portion are defined by the loops 22 and 23. The material forming these loops is extended on the opposite side of the strips to form legs as shown at 24 and 25. These may be shoved into the ground in the manner of stakes, with the vertical position of the control strip being readily adjustable by the degree of penetration of the legs in the ground. The engagement of the central portion 21 with the reinforcing channel 19 of the control strip is preferably with some degree of a forced fit, and the resulting installation will have sufficient solidity to withstand the treatment it will inevitably receive during the pouring of the concrete. The legs 24 and 25 are preferably stiffened by forming them into a curvature in cross section, as shown in FIGURE 2. In this preferred form, the entire unit can be manufactured from a single strip of steel.

The supporting devices 20 are preferably installed on approximately twelve inch centers, and the width of the strip of which the supports are formed may conveniently amount to approximately three quarters of an inch. At least three inches of penetration into the ground 11 should be provided, and the vertical depth of the strips 15 is preferably approximately an inch and a quarter. The top edge of these strips is preferably established at a quarter of an inch, and the bottom somewhat more than that to provide a slight convergence of the side surfaces of the strip.

Referring to FIGURE 6, the wall 26 may be considered as composed of the portions 26a and 26b on opposite sides of the crack plane established by the parallel control strips 27 and 28, which have been secured to the opposite form panels (not shown) that determined the surfaces of the concrete structure. The wall is provided with vertical reinforcing rods as shown at 29, and with horizontal rods as shown at '30. The horizontal rods 30 are interrupted at the plane determined by the strips 27 and 28, and auxiliary rods 31 are preferably installed at an angle of approximately sixty degrees to the plane established by the strips 27 and 28. These auxiliary rods extend approximately equally on either side of this plane, and are undulated as shown to provide for maximum retention in the concrete per unit of length, and also to provide some limited degree of extensibility at the plane of crack formation. The presence of these auxiliary rods will tend to inhibit a lateral and also a vertical shifting of the portions 26a and 26b with respect to each other, and also will tend to restrain the horizontal separation of these portions. The appearance of the crack will be concealed by the presence of the strips 27 and 28, and the structural integrity of the entire installation will be substantially preserved. This same effect may be obtained for horizontal slabs provided with the control strips as shown at 12-14 in FIGURE 1 by positioning auxiliary undulated rods in a generally horizontal plane at the position as shown at 32 in FIG- URE 2, with these rods being laid approximately sixty degrees to a vertical plane passing along the strip 14. The spacing of these auxiliary rods along the strip will be influenced by an estimate of the surrounding conditions that will effect the formation and enlargement of the cracks. In the wall structure shown in FIGURE 6, these auxiliary reinforcing rods are preferably placed on approximately twelve inch centers.

The particular embodiments of the present invention which have been illustrated and discussed herein are for illustrative purposes only and are not to be considered as a limitation upon the scope of the appended claims. In these claims, it is my intent to claim the entire invention disclosed herein, except as I am limited by the prior art.

I claim:

1. A concrete structure comprising a mass of concrete extending on opposite sides of a plane defined by at least one crack-forming device; and

a plurality of substantially parallel auxiliary rod means exclusively extending across said plane at an angle thereto of substantially less than ninety degrees, and embedded in the said concrete on the opposite sides of said plane, all of said rods extending in the same direction.

2. A structure as defined in claim 1, wherein said auxiliary rod means consists of undul-ated rods.

3. A structure as defined in claim 1, wherein said auxiliary rod means is disposed at an angle of substantially sixty degrees to said plane.

4. A structure as defined in claim 1, wherein said crackforming device includes a pair of parallel strips embedded in the said mass of concrete on opposite sides thereof.

References Cited UNITED STATES PATENTS 767,582 8/1904 Lewman 52378 985,891 3/1911 Fox 52370 1,638,473 8/1927 Cochrane 52-396 X 1,641,109 8/1927 Wilson 94-8 1,863,846 6/1932 Heltzel 94l8 2,118,340 5/1938 Burgess 9418 2,139,465 12/1938 Robertson 9418 2,695,513 11/1954 Williams 52-396 X FOREIGN PATENTS 532,236 1/1941 Great Britain. 861,251 2/ 1961 Great Britain.

FRANK L. ABBOTT, Primary Examiner.

ALFRED C. PERHAM, Examiner. 

